One of the primary ways to get herbs is through Farming them. There are two herb patches within Great Kourend and the Kebos Lowlands: one in Hosidius and one in the Farming Guild. Herb farming runs can be started at low Farming and Herblore levels, and only improve in speed and efficiency over time. Farming is also the only reliable way to get large amounts of a specific herb, which can be useful if the player needs a specific type of potion for combat or other training. There are a number of ways to get herb seeds to farm, such as from Farming contracts, thieving master farmers, and from various monster drops. At high Thieving levels, master farmers are a good option for dedicated herb seed collection, providing up to 170k Herblore experience worth of seeds in an hour of pickpocketing.
Combat
Another common source of herbs is through combat, oftentimes through training Slayer. Common monsters like deviant spectres consistently drop grimy herbs, allowing for either dedicated herb collection by killing them or passive herb collection while training Slayer. If possible, it is recommended to bring a herb sack while killing monsters that drop large amounts of grimy herbs, to allow for longer trips and more herbs to be collected. Additionally, completing the Chambers of Xeric has a chance of rewarding significant amounts of noted herbs, which can be a nice source of bonus Herblore experience while raiding.
While not a great source, the Wintertodt will give small amounts of herbs while training Firemaking. The exact type and amount of herbs is dependent on the player's Herblore level. The amount of herbs rewarded from this activity is not significant enough to rely on for long-term training, but it can be a good way to get some early Herblore levels while training other skills at the Wintertodt.
Ground from bird nests. The only way to obtain Bird nests is through a lucky drops while training Woodcutting. Saradomin brews can also be obtained from the grubby chest in the Forthos Dungeon.